Inducer, and inducer-equipped pump

ABSTRACT

The present invention is concerned with an axial-flow or mixed-flow inducer ( 3 ) which is disposed upstream of a main impeller ( 2 ) for improving the suction capability of a pump such as a turbopump. In the inducer ( 3 ), a blade angle (β bt ) from a tip (T 1 ) to a hub (H 1 ) at a blade leading edge ( 31 ) is substantially the same as an inlet flow angle (β 1-t ) at a designed flow rate.

TECHNICAL FIELD

The present invention relates to an inducer and a pump with an inducer,and more particularly to an axial-flow or mixed-flow inducer which isdisposed upstream of a main impeller with its axis aligned with an axisof the main impeller for improving the suction capability of a pump suchas a turbopump, and a pump with such an inducer.

BACKGROUND ART

Heretofore, it has been customary to mount an inducer on the distal endof the shaft of a pump for improving the suction capability of the pump.For example, an inducer disposed upstream of a centrifugal main impellercomprises an axial-flow or mixed-flow impeller which has configurationalcharacteristics in that it has less blades and a longer blade lengththan ordinary impellers. The inducer is disposed upstream of the mainimpeller with its rotational axis aligned with the main impeller, and isrotated by the shaft at the same rotational speed as the main impeller.

Conventional inducers have blades designed to be of a helical shape. Inthe cross-sectional shape of blades, the tip, hub, and shaft center arepositioned in line. According to a conventional process of designinginducers, a blade angle is designed only along the tip, and a bladeangle is determined along the hub by helical conditions. The tip bladeangle on the blade leading edge of a conventional inducer is designed tobe greater than an inlet flow angle which is calculated from an axialinflow velocity of the flow in the inlet at a designed flow rate and acircumferential blade speed. The differential angle between the bladeangle along the tip on the blade leading edge and the inlet flow angleis referred to as an incidence angle. The incidence angle is normallydesigned to be in a range from 35% to 50% of the blade angle on theblade leading edge. A blade angle from the inlet (leading edge) to theoutlet (trailing edge) of the tip of the inducer is designed to beconstant or to increase stepwise, linearly, or quadratically in order tomeet a head required for the inducer.

When an inducer thus shaped is mounted in place, even if the pressureupstream of the inlet of the blades, i.e., the pressure of a fluid in anupstream region of the pump impeller, drops locally to a level that isequal to or lower than a saturated vapor pressure, thereby causingcavitation, a flow passage following a throat of the inducer isprevented from being closed by the cavitation, and the pressure of theliquid can be increased though the cavitation is developed. With theinducer disposed upstream of the main impeller, the suction capabilityof the pump can be improved as compared to a case where a centrifugalmain impeller were used alone, and the pump can operate at a higherspeed and can be smaller in size.

However, as described above, since the tip blade angle on the bladeleading edge of a conventional inducer is designed to have an incidenceangle to the flow in the inlet at a designed flow rate, and to be shapedsuch that a distribution of tip blade angles from the inlet to theoutlet is constant or increases. Therefore, loads concentrate in thevicinity of the inlet of the inducer, tending to develop a reverse flowat the inlet. If the pump is operated in a partial flow rate range whichis lower than the designed flow rate, then since the incidence angle atthe inlet of the inducer becomes larger, the reverse flow developed atthe inlet also becomes larger in scale. If a reverse flow is developedat the inlet while cavitation is being produced, the cavitationinterferes with an upstream component, which tends to be damaged by theimpact pressure of the cavitation.

Furthermore, the cavitation is generated and eliminated repeatedly at alow frequency within the reverse flow at the inlet, causing the pump tovibrate greatly in its entirety. In pumps for liquid hydrogen, thethermodynamic effect of hydrogen which acts to improve the suctioncapability is reduced by the reverse flow at the inlet, resulting in areduction in the suction capability of the pump.

In view of the above drawbacks, it is of practical importance to designan inducer capable of suppressing the occurrence of a reverse flow atthe inlet. Heretofore, attempts have been made to improve the bladeangle, blade length, number of blades, and blade tip shape of inducersin order to satisfy the suction capability and a required head. However,efforts have not been made so far to improve the blade shape of inducersfor suppressing a reverse flow at the inlet. At present, consequently,there have not yet been developed inducers for suppressing a reverseflow at the inlet while satisfying a required head and the suctioncapability.

DISCLOSURE OF INVENTION

The present invention has been made in view of the above conventionaldrawbacks. It is an object of the present invention to provide aninducer and a pump with an inducer which are highly reliable and capableof suppressing a reverse flow at the inlet while satisfying a requiredhead and the suction capability.

In order to solve the conventional drawbacks, according to a firstaspect of the present invention, there is provided an inducer disposedupstream of a main impeller, characterized in that a blade angle from atip to a hub at a blade leading edge is substantially the same as aninlet flow angle at a designed flow rate.

Since the blade angle at the blade leading edge is substantially thesame as the inlet flow angle, an incidence angle of the flow at a flowrate ranging from the designed flow rate to a partial flow rate isreduced, making it possible to effectively suppress a reverse flow atthe inlet.

According to a preferred aspect of the present invention, a blade angledistribution on the tip from the blade leading edge to a blade trailingedge is such that a rate of reduction of the blade angle toward theblade leading edge is greater upstream of a region in the vicinity of athroat than downstream of the region in the vicinity of the throat, anda rate of change of the blade angle is smaller in a range from theregion in the vicinity of the throat toward a region in the vicinity ofa distance 0.9 in a non-dimensional flow direction than upstream of theregion in the vicinity of the throat. The throat refers to an inletportion of a passage that is defined by a suction surface of a blade andan adjacent blade.

By thus making the rate of reduction of the blade angle toward the bladeleading edge upstream of the region in the vicinity of the throat largerthan downstream of the region in the vicinity of the throat, and alsomaking the rate of change of the blade angle in the range from theregion in the vicinity of the throat toward the region in the vicinityof the distance 0.9 in the non-dimensional flow direction smaller thanupstream of the region in the vicinity of the throat, the load can bedistributed entirely along the tip, and a large pressure drop region onthe suction surface can be brought upstream of the throat. Therefore,most of the cavitation is generated in a front half of the suctionsurface of the inducer blade, and the flow passage following the throatis unlikely to be closed, allowing the pump to have a sufficient suctioncapability. Since the load is distributed on the entire blade along thetip, a sufficient head can be maintained.

According to a preferred aspect of the present invention, a blade angledistribution on the hub from the blade leading edge to the bladetrailing edge has an inflection point in the vicinity of the throat, andis such that a rate of change of the blade angle is smaller upstream ofthe throat, and a rate of increase of the blade angle is larger alongthe direction of a flow downstream of the throat.

By thus making the rate of change of the blade angle smaller along thehub in the direction of the flow upstream of the throat, and also makingthe rate of increase of the blade angle larger along the hub in thedirection of the flow downstream of the throat, the load can bedistributed entirely on the blade along the hub, and a required head canbe maintained.

According to a second aspect of the present invention, there is provideda pump with an inducer, characterized in that the pump has a mainimpeller mounted on a rotatable shaft, and the inducer is disposedupstream of the main impeller so as to align its axis with an axis ofthe main impeller.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view showing a portion of a turbopumpincorporating an inducer according to an embodiment of the presentinvention;

FIG. 2 is a perspective view of the inducer shown in FIG. 1;

FIG. 3A is an external view showing a tip blade angle of the induceraccording to the present invention, FIG. 3B an external view showing ahub blade angle, and FIG. 3C a view showing the relationship between anincidence angle, an inlet flow angle, and a tip blade angle;

FIG. 4A is a meridional cross-sectional view of the inducer according tothe present invention, and FIG. 4B is a perspective view of the inducershown in FIG. 4A;

FIG. 5A is a meridional cross-sectional view of a conventional inducer,and FIG. 5B is a perspective view of the inducer shown in FIG. 5A;

FIG. 6A is a graph showing tip blade angle distributions from a bladeleading edge to a blade trailing edge of the inducer according to thepresent invention and a conventional inducer, respectively, and FIG. 6Bis a graph showing hub blade angle distributions of the induceraccording to the present invention and the conventional inducer,respectively;

FIGS. 7A and 7B are graphs showing fluid velocity distributions betweenthe hub and the tip at a flow rate which is 75% of a designed flow rateat a position that is 5 mm upstream of the blade leading edge of theinducer according to the present invention and the conventional inducer,FIG. 7A showing the fluid velocity distributions in the circumferentialdirection, and FIG. 7B the fluid velocity distributions in an axialdirection;

FIGS. 8A and 8B are graphs showing static pressure distributions on ablade surface along the tip at the designed flow rate, FIG. 8A showingthe static pressure distributions of the conventional inducer, and FIG.8B the static pressure distributions of the inducer according to thepresent invention;

FIGS. 9A and 9B are graphs showing measured data of fluid velocitydistributions at a flow rate which is 75% of the designed flow rate ofthe inducer according to the present invention and the conventionalinducer, FIG. 9A showing the measured data of fluid velocitydistributions in the circumferential direction, and FIG. 9B the measureddata of fluid velocity distributions in the axial direction;

FIG. 10 is a graph showing measured data of the suction capabilities ata flow rate which is 75% of the designed flow rate of the induceraccording to the present invention and the conventional inducer; and

FIGS. 11A and 11B are diagrams showing the manner in which cavitation isdeveloped upstream of a blade leading edge at a flow rate which is 75%of the designed flow rate and a cavitation number of 0.08, FIG. 11Ashowing the measured data of the conventional inducer, and FIG. 11B themeasured data of the inducer according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of an inducer and a pump with an inducer according to thepresent invention will be described in detail below with reference tothe drawings. FIG. 1 is a cross-sectional view showing a portion of aturbopump incorporating an inducer according to an embodiment of thepresent invention, and FIG. 2 is a perspective view of the inducer shownin FIG. 1. The turbopump shown in FIG. 1 has a rotatable shaft 1, a mainimpeller 2 mounted on the shaft 1, and an inducer 3 disposed upstream ofthe main impeller 2. The inducer 3 has an axis in alignment with theaxis of the main impeller 2. When the shaft 1 rotates, the inducer 3rotates at the same rotational speed as the main impeller 2. The inducer3 has a plurality of blades. In FIG. 2, the inducer 3 is shown as havingthree blades.

A working fluid of the pump flows into the inducer 3 in the directionindicated by the arrow F in FIG. 1. The working fluid that has flowedinto the inducer 3 has its pressure increased while generatingcavitation in the inducer 3. When the working fluid flows into thedownstream main impeller 2, the pressure of the working fluid is furtherincreased to a head required by the pump. Since the pressure of theworking fluid is increased to a level high enough not to generatecavitation in the main impeller 2, the suction capability of the pump isimproved as compared to a case where the main impeller 2 is used alone.

The inducer 3 according to the present invention has the followingconfigurational features:

(1) The blade angle from a tip T₁ to a hub H₁ on a blade leading edge 31is substantially the same as the inlet flow angle at the designed flowrate.

(2) A blade angle distribution on the tip T₁ from the blade leading edge(inlet) 31 to a blade trailing edge (outlet) 32 is such that a rate ofreduction of the blade angle toward the blade leading edge 31 is greaterupstream of a region in the vicinity of the throat than downstream ofthe region in the vicinity of the throat, and a rate of change of theblade angle is smaller in a range from the region in the vicinity of thethroat toward a region in the vicinity of a distance 0.9 in anon-dimensional flow direction than upstream of the region in thevicinity of the throat. The blade angle on the tip T₁ (tip blade angle)means an angle indicated by β_(bt) in FIG. 3A.

(3) A blade angle distribution on the hub H₁ from the blade leading edge(inlet) 31 to the blade trailing edge (outlet) 32 has an inflectionpoint in the vicinity of the throat, and is such that a rate of changeof the blade angle is small along the direction of the flow upstream ofthe throat, and a rate of increase of the blade angle is largedownstream of the throat. The blade angle on the hub HI (hub bladeangle) means an angle indicated by β_(bh) in FIG. 3B. In FIG. 3B, theblades of the inducer are shown by the dotted lines.

The inducer according to the present invention which has the aboveconfigurational features and a conventional inducer were actuallydesigned under the conditions described below, and the inducer accordingto the present invention and the conventional inducer were compared withrespect to their operation. FIG. 4A is a meridional cross-sectional viewof the inducer 3 according to the present invention which was designed,and FIG. 4B is a perspective view of the inducer 3. FIG. 5A is ameridional cross-sectional view of the conventional inducer 103 whichwas designed, and FIG. 5B is a perspective view of the conventionalinducer 103.

In designing the inducers 3 and 103, design requirements included arotational speed N=3000 min⁻¹, a flow rate Q=0.8 m³/min, and a head H=2m, and these design requirements were the same for the conventionalinducer 103 and the inducer 3 according to the present invention. Themeridional shapes of the inducers 3 and 103 are of the fully axial-flowtype. In the meridional cross-sectional views of FIGS. 4A and 5A, bladeleading edges 31 and 131 and blade trailing edges 32 and 132 arerepresented by straight lines perpendicular to the flow direction F.

In the inducers 3 and 103, tips T₁ and T₀ had a diameter D_(t)=89 mm,and hubs H₁ and H₀ had a diameter D_(h)=30 mm. The conventional inducer103 had a blade length L₀=50 mm in the axial direction on a meridionalplane, and the inducer according to the present invention 3 had a bladelength L₁=35 mm in the axial direction on a meridional plane. Theconventional inducer 103 and the inducer 3 according to the presentinvention had the same actual blade length along the tip.

The conventional inducer 103 was a planar helical inducer having thesame blade angle from the blade leading edge 131 to the blade trailingedge 132, and the blade angle on the tip To was designed such that theincidence angle was 35% of the blade angle at the blade leading edge131. The inducer according to the present invention 3 was designed suchthat the blade angle at the blade leading edge 31 from the tip T₁ to thehub H₁ is substantially the same as the inlet flow angle at the designedflow rate.

An axial velocity V_(x) of the inlet flow at the designed flow rate isdetermined from the meridional shape of the inducer and the designrequirements according to the following equation (1): $\begin{matrix}{V_{x} = {\frac{Q/60}{\frac{\pi}{4}\left( {D_{t}^{2} - D_{h}^{2}} \right)} = {\frac{0.8/60}{\frac{3.141592}{4}\left( {0.089^{2} - 0.030^{2}} \right)} = {2.42\left\lbrack {m\text{/}s} \right\rbrack}}}} & (1)\end{matrix}$

A circumferential rotational velocity V_(θ-t) of the inducer blade atthe tip is determined according to the following equation (2):$\begin{matrix}{V_{\theta - t} = {\frac{{\pi D}_{t}N}{60} = {\frac{3.141592 \times 0.089 \times 3000}{60} = {13.98\left\lbrack {m\text{/}s} \right\rbrack}}}} & (2)\end{matrix}$

The inlet flow angle β_(1-t) at the tip is determined according to thefollowing equation (3):β_(1-t)=Tan⁻¹(V _(x) /V _(θ-t))=Tan⁻¹(2.42/13.98)=9.82[deg]  (3)

The inducer 3 according to the present invention is formed such that theblade angle of the blade leading edge 31 on the tip T₁ is substantiallythe same as the inlet flow angle β_(1-t) at the designed flow rate. Withrespect to the conventional inducer, the tip blade angle β_(b0-t) isdesigned such that the incidence angle is 35% of the tip blade angleβ_(b0-t). The incidence angle, the inlet flow angle B_(1-t), and the tipblade angle B_(b0-t) are related to each other as shown in FIG. 3C. Theincidence angle is an angle produced by subtracting the inlet flow angleB_(1-t) from the tip blade angle B_(b0-t). That is, the tip blade angleβ_(b0-t) in the conventional inducer is determined according to thefollowing equation (4):β_(b0-t)−β_(1-t)=0.35β_(b0-t)(1−0.35) β_(b0-t)=β_(b0-t)β_(b0-t)=β_(1-t)(1−0.35)=9.82/0.65≈15 [deg]  (4)

The hub blade angle β_(b0-h) in the conventional inducer is determinedfrom the helical conditions according to the following equation (5):$\begin{matrix}{\beta_{{b0} - h} = {{{Tan}^{- 1}\left( {{\frac{D_{t}}{D_{h}} \cdot \tan}\quad\beta_{{b0} - t}} \right)} = {{{Tan}^{- 1}\left( {{\frac{0.089}{0.030} \cdot \tan}\quad 15} \right)} = {38.5\left\lbrack \deg \right\rbrack}}}} & (5)\end{matrix}$

FIG. 6A is a graph showing tip blade angle distributions from the bladeleading edge to the blade trailing edge of the inducer according to thepresent invention and the conventional inducer, respectively, and FIG.6B is a graph showing hub blade angle distributions of the induceraccording to the present invention and the conventional inducer,respectively. In FIGS. 6A and 6B, the horizontal axis represents thenon-dimensional meridional location normalized by the distance from theleading edge to trailing edge on the meridional plane. In FIG. 6A, thevertical axis represents the tip blade angle. In FIG. 6B, the verticalaxis represents the hub blade angle.

As shown in FIGS. 6A and 6B, the inducer according to the presentinvention has a three-dimensional blade shape such that the blade anglechanges continuously from the blade leading angle (inlet) to the bladetrailing edge (outlet), and the tip blade angle and the hub blade anglechange differently from each other. In order to design athree-dimensional blade shape for an inducer in which the blade angle atthe blade leading edge is substantially the same as the inlet flow angleand which meets the required design requirements, it is preferable touse a three-dimensional inverse method. The three-dimensional inversemethod is a method proposed by Dr. Zangeneh of UCL (University CollegeLondon) in 1991. The three-dimensional inverse method is a design methodfor defining a loading distribution on the blade surface and determininga blade surface shape that meets the loading distribution according tonumerical calculations. Details of the three-dimensional inverse methodare described in a known document (Zangeneh, M., 1991, “A CompressibleThree-Dimensional Design Method for Radial and Mixed Flow TurbomachineryBlades”, Int. J. Numerical Methods in Fluids, Vol. 13. pp. 599-624).

The inducer according to the present invention was designed according tothe three-dimensional inverse method. In the three-dimensional inversemethod, entire blade loading was inputted such that the designrequirements would be the same as those of the conventional inducer, ablade loading distribution was inputted such that the loading on the tipand hub blade leading edges are zero, and a fore loading distributionwas inputted such that the loading would concentrate on a front portionas a whole. As a result of the designing process according to thethree-dimensional inverse method, the inducer according to the presentinvention was designed such that the blade angle from the tip to the hubon the blade leading edge was substantially the same as the inlet flowangle at the designed flow rate, so that the incidence angle of the flowwas 0°. Because of the configurational feature that makes the bladeangle on the blade leading edge substantially equal to the inlet flowangle, the incidence angle of the flow at a flow rate range from thedesigned flow rate to a partial flow rate is reduced, making it possibleto effectively suppress a reverse flow at the inlet.

As shown in FIG. 6A, the tip blade angle distribution from the bladeleading edge to the blade trailing edge of the inducer according to thepresent invention is such that a rate of reduction of the blade angletoward the blade leading edge is larger upstream of the region in thevicinity of the throat than downstream of the region in the vicinity ofthe throat, and a rate of change of the blade angle is smaller in arange from the region in the vicinity of the throat toward the region inthe vicinity of the distance 0.9 in the non-dimensional flow directionthan upstream of the region in the vicinity of the throat. By thusmaking the rate of reduction of the blade angle toward the blade leadingedge upstream of the region in the vicinity of the throat larger thandownstream of the region in the vicinity of the throat, and also makingthe rate of change of the blade angle in the range from the region inthe vicinity of the throat toward the region in the vicinity of thedistance 0.9 in the non-dimensional flow direction smaller than upstreamof the region in the vicinity of the throat, the blade loading can bedistributed entirely along the tip, and a large pressure drop region onthe suction surface can be brought upstream of the throat. Therefore,most of the cavitation is generated in a front half of the suctionsurface of the inducer blade, and the flow passage following the throatis unlikely to be closed, allowing the pump to have a sufficient suctioncapability. Since the blade loading is distributed on the entire bladealong the tip, a sufficient head can be maintained.

As shown in FIG. 6B, the hub blade angle distribution from the bladeleading edge to the blade trailing edge of the inducer according to thepresent invention has an inflection point in the vicinity of the throat,and is such that a rate of change of the hub blade angle is smalleralong the direction of the flow upstream of the region in the vicinityof the throat than downstream of the region in the vicinity of thethroat, and a rate of increase of the hub blade angle is largerdownstream of the region in the vicinity of the throat than upstream ofthe region in the vicinity of the throat. By thus making the rate ofchange of the blade angle smaller along the hub in the direction of theflow upstream of the throat, and also making the rate of increase of theblade angle larger along the hub in the direction of the flow downstreamof the throat, the blade loading can be distributed entirely on theblade along the hub, and a required head can be maintained.

The inducer according to the present invention and the conventionalinducer were analyzed for a flow field therearound by computationalfluid dynamics. The results of the analysis will be described below.

FIGS. 7A and 7B are graphs showing fluid velocity distributions betweenthe hub and the tip at a flow rate which is 75% of the designed flowrate at a position that is 5 mm upstream of the blade leading edge ofthe inducer according to the present invention and the conventionalinducer, FIG. 7A shows the fluid velocity distributions in thecircumferential direction, and FIG. 7B shows the fluid velocitydistributions in the axial direction. In FIGS. 7A and 7B, the horizontalaxis represents the non-dimensional radial location normalized by thedistance from the hub to the tip. In FIG. 7A, the vertical axisrepresents the non-dimensional circumferential velocity which isindicative of the circumferential velocity of the flow as normalized bythe circumferential velocity of the tip of the inducer blade. In FIG.7B, the vertical axis represents the non-dimensional axial velocitywhich is indicative of the axial velocity of the flow as normalized bythe circumferential velocity of the tip of the inducer blade.

As shown in FIG. 7A, since the conventional inducer produces a reverseflow at the inlet, the circumferential velocity of the fluid on the tipis increased by the reverse flow at the inlet. As shown in FIG. 7B,since the axial velocity of the fluid in the conventional inducer is ofa negative value in the vicinity of the tip, there is a region where areverse flow is developed.

With the inducer according to the present invention, however, since theblade angle from the tip to the hub at the blade leading edge issubstantially the same as the inlet flow angle at the designed flowrate, a reverse flow is unlikely to be developed at the inlet. Even at aflow rate which is 75% of the designed flow rate, there is no fluidvelocity distribution representing a reverse flow at the inlet as withthe conventional inducer (see FIGS. 7A and 7B).

FIG. 8A shows static pressure distributions on the blade surfaces (thepressure surface and the suction surface) along the tip at the designedflow rate of the conventional inducer, and FIG. 8B shows static pressuredistributions on the blade surfaces (the pressure surface and thesuction surface) along the tip at the designed flow rate of the induceraccording to the present invention. In FIGS. 8A and 8B, the horizontalaxis represents the non-dimensional meridional location normalized bythe distance from the leading edge to trailing edge on the meridionalplane, and the vertical axis represents the static pressure coefficient.The pressure surface refers to a downstream blade surface, and thesuction surface refers to an upstream blade surface.

As described above, because of the incidence angle between the tip bladeangle and the inlet flow angle of the conventional inducer, as shown inFIG. 8A, the static pressure on the suction surface largely drops at theblade leading edge (inlet), and is widely different from the staticpressure on the pressure surface. Because of this pressure distributionof the conventional inducer, it is expected that intensive cavitation isgenerated in the vicinity of the blade leading edge when the pressure onthe blade leading edge (inlet) drops, but the flow passage following thethroat is not closed.

With the inducer according to the present invention, as shown in FIG.8B, a drop in the static pressure on the suction surface at the bladeleading edge (inlet) is small, and the static pressure restores thelevel at the blade leading edge up to the throat. Because of thispressure distribution of the inducer according to the present invention,it is expected that weak cavitation is generated on the blade surfaceupstream of the throat when the pressure on the blade leading edge(inlet) drops, but the flow passage following the throat is not closed,and the inducer according to the present invention has a suctioncapability equivalent to that of the conventional inducer.

With the conventional inducer, the loading on the blade surfaces (thestatic pressure difference between the pressure surface and the suctionsurface) concentrates in the vicinity of the blade leading edge (inlet),with almost no load being imposed downstream (see FIG. 8A). However, theloading on the blade surfaces of the inducer according to the presentinvention is distributed entirely from the blade leading edge (inlet) tothe blade trailing edge (outlet) (see FIG. 8B). Thus, it is expectedthat the inducer according to the present invention is capable ofachieving the same head as the conventional inducer though the tip bladeangle of the inducer according to the present invention is smaller as awhole than the tip blade angle of the conventional inducer (see FIG.6A).

The conventional inducer and the inducer according to the presentinvention as described above were actually fabricated, and measured on atesting device for a circumferential velocity distribution of the fluidand an axial velocity distribution of the fluid between the hub and thetip, using a three-hole Pitot tube positioned 5 mm upstream of the bladeleading edge of the inducer. FIGS. 9A and 9B are graphs showing fluidvelocity distributions at a flow rate which is 75% of the designed flowrate, FIG. 9A shows the fluid velocity distributions in thecircumferential direction, and FIG. 9B shows the fluid velocitydistributions in the axial direction. In FIGS. 9A and 9B, the horizontalaxis represents the non-dimensional meridional radial locationnormalized by the distance from the hub to the tip. In FIG. 9A, thevertical axis represents the non-dimensional circumferential velocitywhich is indicative of the circumferential velocity of the flow asnormalized by the circumferential velocity of the tip of the inducerblade. In FIG. 9B, the vertical axis represents the non-dimensionalaxial velocity which is indicative of the axial velocity of the flow asnormalized by the circumferential velocity of the tip of the inducerblade.

As shown in FIGS. 9A and 9B, since the conventional inducer produces areverse flow at the inlet, the circumferential velocity of the fluid onthe tip is increased by the reverse flow at the inlet. It was confirmedthat the axial velocity of the fluid in the conventional inducer is of anegative value in the vicinity of the tip, and there is a region where areverse flow is developed. With the inducer according to the presentinvention, however, even at a flow rate which is 75% of the designedflow rate, there was not confirmed any fluid velocity distributionrepresenting a reverse flow at the inlet as with the conventionalinducer. It can be understood from the above results that a reverse flowat the inlet can be suppressed in the inducer according to the presentinvention than in the conventional inducer.

FIG. 10 shows measured data of the suction capabilities at a flow ratewhich is 75% of the designed flow rate. In FIG. 10, the horizontal axisrepresents a cavitation number where the pressure level at the bladeleading edge (inlet) is made non-dimensional, and the vertical axisrepresents a head coefficient where the head of the inducer is madenon-dimensional. The graph shown in FIG. 10 indicates variation of thehead of the inducer when the pressure level at the blade leading edge(inlet) lowered. When the cavitation number decreases, cavitation isdeveloped in the inducer, lowering the head as shown in FIG. 10. Thegraph shown in FIG. 10 reveals that the suction capability of the pumpis so high that the head coefficient is not lowered at a lowercavitation number.

As shown in FIG. 10, the head of the inducer according to the presentinvention is almost the same as the head of the conventional inducerwhen the cavitation number is high, and the cavitation number of theinducer according to the present invention is almost the same as thecavitation number of the conventional inducer when the head dropssharply. It can be seen from these measured data that the induceraccording to the present invention has the same head and suctioncapability as the conventional inducer.

FIGS. 11A and 11B are diagrams showing the manner in which cavitation isdeveloped upstream of the blade leading edge at a flow rate which is 75%of the designed flow rate and a cavitation number of 0.08, FIG. 11Ashows the measured data of the conventional inducer, and FIG. 11B showsthe measured data of the inducer according to the present invention.

As shown in FIG. 11A, in the conventional inducer, intensive cavitation140 is developed in the vicinity of the blade leading edge (inlet) 131,and the cavitation 140 is present upstream of the blade leading edge 131due to a reverse flow at the inlet. In the inducer according to thepresent invention, cavitation 40 weaker than in the conventional induceris developed on the blade surface from the blade leading edge (inlet) 31to the throat, but cavitation due to a reverse flow at the inlet is notessentially present upstream of the blade leading edge 31. The induceraccording to the present invention is thus more effective to suppress areverse flow at the inlet as compared to the conventional inducer, hasthe flow passage following the throat prevented from being closed bycavitation, and can achieve the same suction capability as theconventional inducer.

Although a certain embodiment of the present invention has beendescribed, it should be understood that the present invention is notlimited to the above embodiment, but various changes and modificationsmay be made within the scope of the technical concept of the invention.

As described above, the inducer according to the present inventionmaintains a high suction capability because a reverse flow produced atthe inlet is suppressed and cavitation tends to be developed upstream ofthe throat and is unlikely to close the flow passage. Since the bladeloading is distributed entirely on the blade surfaces, the inducer canmaintain a high head. As a result, a pump combined with the induceraccording to the present invention which is positioned upstream of acentrifugal main impeller is free of conventional drawbacks such asdamage and vibration of upstream components, caused by a reverse flow atthe inlet, and a reduction in the suction capability, and is highlyreliable.

INDUSTRIAL APPLICABILITY

The present invention is applicable to an axial-flow or mixed-flowinducer disposed upstream of a main impeller for improving the suctioncapability of a pump such as a turbopump.

1. An inducer disposed upstream of a main impeller, characterized inthat a blade angle distribution on said tip from the blade leading edgeto a blade trailing edge is such that a rate of reduction of said bladeangle toward said blade leading edge is greater upstream of a region inthe vicinity of a throat than downstream of the region in the vicinityof said throat, and a rate of change of said blade angle is smaller in arange from the region in the vicinity of the throat toward a region inthe vicinity of a distance 0.9 in a non-dimensional flow direction thanupstream of the region in the vicinity of said throat.
 2. (canceled) 3.The inducer according to claim 1, characterized in that a blade angledistribution on said hub from the blade leading edge to the bladetrailing edge has an inflection point in the vicinity of the throat, andis such that a rate of change of the blade angle is small upstream ofthe throat, and a rate of increase of the blade angle is large along thedirection of a flow downstream of said throat.
 4. A pump with aninducer, characterized in that said pump having a main impeller mountedon a rotatable shaft; and said inducer according to any one of claim 1or 3 is disposed upstream of said main impeller so as to align its axiswith an axis of said main impeller.